Method of removing filler materials



Oct. 3, w HALL METHOD OF REMOVING FILLER MATERIALS Filed Aug. 8, 195a \D u gzls (1)6650/2, INV EN TOR BY ugh? ATTOFZN EYS United States Patent This invention relates to a method of removing a metallic filler from the interior of an object which may be an object of metal.

The invention is particularly applicable to any forged, extruded or moulded objects in which internal cavities or passages are filled with a metallic filler material which is subsequently to be removed.

Particularly, but not exclusively, the invention relates to a process of manufacturing blades of internal combustion turbine engines which blades may be of nickel base alloy and have interior cavities or passages. lln making such blade a ferrous metal such as mild steel may be used as a filler in the cavities or passage in the billet to control the shape of the cavities or passage during the extrusion of the billet and, after extrusion, the filler has to be removed.

In normal practice material to be removed by electrolysis is made the anode. The present invention is based on the discovery that where nitric acid is used to remove the filler it is advantageous to make the material to be removed the cathode.

According to this invention the material to be removed is immersed in an electrolyte containing nitric acid, an anode is placed in the electrolyte and an electric current is passed through the electrolyte in a circuit in which the material to be removed constitutes at least part of the cathode.

Preferably the electrolyte consists of nitric acid diluted in water. The water should be carefully filtered to exclude foreign matter and is preferably distilled- A suitable concentration is by volume of nitric acid in water.

The anode may be for example of platinum or stainlens steel but as these metals will gradually be decomposed, it is preferred to use an anode of graphite enclosed in a porous ceramic pot. lAHy particles of the graphite which become detached will be caught by the pot and the pot does not alfect the electrolytic action.

Only suflicient voltage is required in the circuit to reverse the normal voltage which would otherwise exist, that is sufiicient to pass a current of about one ampere through the electrolyte.

An example of this invention is illustrated diagrammatically in the accompanying drawing.

A bath 10 filled with electrolyte is provided in which 3,002,908 Patented Oct. 3, 1961 is placed an internal combustion turbine blade 11 of nickel base alloy having passages therein filled with mild steel filler 12. Also inserted in the bath is a block of graphite 13 contained in a porous ceramic pct 14. The graphite block which is insoluble is connected to the positive pole of a battery 15 and the blade to the negative pole of the battery.

The mild steel filler acts as the cathode and hydrogen released at the cathode stirs up the nitric acid adjacent the mild steel and enhances the action of the acid in removing the mild steel. Nascent hydrogen produced during electrolysis is also believed to reduce the oxide film which may be formed on the mild steel and which would normally interfere with the action of the acid upon the steel, the gases released by electrolysis agitating and cleaning the surface of the mild steel filler allowing the acid to do its work of decomposition. In this case the whole blade forms the cathode and not merely the filler material, but the blade by reason of its nickel base composition will not be subject to the decomposive action which acts on the filler:

I claim: I

1. A process of removing ferrous metal filler from the interior of an object made of a nickel base material: comprising the steps of immersing the object in a nitric acid electrolyte; placing an insoluble anode in the electrolyte; and passing an electric current between the anode and the object, which is made cathode, through the electrolyte; the object and the filler being both exposed to the electrolyte, and being the cathode throughout the process.

2. The process of claim 1 in which the filler is a mild steel and the anode is graphite.

3. The method of removing mild steel filler from internal holes in a nickel base alloy blade intended for an internal combustion turbine engine during the course of the manufacture of said blade, comprising providing a bath containing an electrolyte which contains nitric acid and inserting that part of the blade which contains the filler material in the bath, inserting a piece of graphite enclosed in a porous ceramic pot in the electrolyte, and connecting an electric circuit from a source of electrical energy so that the graphite is continuously the anode and the blade continuously the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,204,391 Allen June 11, 1940 2,374,449 Mulcahy Apr. 24, 1945 2,590,927 Brandt et a1. Apr. 1, 1952 FOREIGN PATENTS 13,666 Great Britain of 1908 

1. A PROCESS OF REMOVING FERROUS METAL FILLER FROM THE INTERIOR OF AN OBJECT MADE OF A NICKEL BASE MATERIAL: COMPRISING THE STEPS OF IMMERSING THE OBJECTING IN A NITRIC ACID ELECTROLYTE, PLACING AN INSOLUBLE ANODE IN THE ELECTROLYTE, AND PASSING AN ELECTRIC CURRENT BETWEEN THE ANODE AND THE OBJECT, WHICH IS MADE CATHODE, THROUGH THE ELECTROLYTE, THE OBJECT AND THE FILLER BEING BOTH EXPOSED TO THE ELECTROLYTE, AND BEING THE CATHODE THROUGHOUT THE PROCESS. 